1. Field of the Invention
This invention relates generally to methods and apparatuses for conducting organic analysis of electrochemical deposition solutions, especially for monitoring organic additive concentrations in electrochemical copper plating baths.
2. Background of the Invention
In the practice of copper interconnect technology in semiconductor manufacturing, electrochemical deposition (ECD) is widely employed for forming copper interconnect structures on microelectronic substrates. The Damascene process, for example, uses physical vapor deposition to deposit a seed layer of copper on a barrier layer, followed by electrochemical deposition of copper.
In the ECD operation, organic additives as well as inorganic additives are employed in the plating solution in which the metal deposition is carried out. The ECD process is sensitive to concentration changes of both the organic and inorganic components. Since concentrations of these components can vary considerably as they are consumed during the life of the bath, it therefore is necessary to conduct real-time monitoring and replenishment of all major bath components to ensure optimal process efficiency and yield of the semiconductor product incorporating the electrodeposited copper.
Inorganic components of the copper ECD bath include copper, sulfuric acid and chloride, which may be measured by potentiometric analysis. Organic additives such as suppressors, accelerators, and levelers are added to the ECD bath to control uniformity of the film thickness across the wafer surface. The concentration of the organic additives can be measured by pulsed cyclic galvanostatic analysis (PCGA), which mimics the plating conditions occurring on the wafer surface. In the practice of the PCGA method, copper is electroplated onto a working or testing electrode, by supplying a sufficient current (or potential), while monitoring the corresponding potential (or current). The electrical potential (or current) measured during such electroplating step correlates with the organic additive concentrations in the sample electroplating bath, and therefore can be used for determining concentrations of organic additives. For further details regarding the PCGA processes, please see U.S. Pat. No. 6,280,602 issued Aug. 28, 2001 to Peter M. Robertson for “Method and Apparatus for Determination of Additives in Metal Plating Baths,” the disclosure of which hereby is incorporated herein by reference for all purposes.
There is a continuing need to improve the PCGA analysis of organic additives in ECD baths and to provide more stable analytical signals and to reduce noise and measurement errors.
There is a further need to modify the conventional PCGA procedures to achieve shorter calibration and measurement cycles, reduce the analysis time, and simplify the hardware and software required for performing the PCGA analysis.
There is still a further need to account for interactions between the different types of organic additives and their impact on the PCGA analysis results.
Other objects and advantages will be more fully apparent from the ensuring disclosure and appended claims.